The present invention relates to preparation of layered double hydroxides exchanged with diisopropylamide (LDH-diisopropylamide) useful as recyclable catalysts for preparing aldols/xcex1,xcex2-unsaturated nitriles/xcex1,xcex2-unsaturated esters/transesterified products/xcex2-nitroalkanols/Michael adducts and epoxides. More particularly the present invention relates to preparation of layered double hydroxides exchanged with diisopropylamide of the formula [MI and/or MII(1xe2x88x92x)MIIIx(OH)2][NCH(CH3)2xe2x88x92]x/2.zH2O wherein MI is a monovalent cation (Li+, Na+, K+, Rb+ or Cs+), MII is a divalent cation (Mg2+, Mn2+Fe2+, Co2+, Ni2+, Cu2+, Zn2+ or Ca2+); MIII is a trivalent ion (Al3+, Cr3+, Mn3+, Fe3+, Co3+, Ni3+, or La3+); x has a value ranging between 0.10 to 0.50 and more preferably 0.20 to 0.33; z is an integer whose values depends on the ingredients and reactions conditions used and methods of preparation and use thereof. The LDH-diisopropylamides of this invention are recyclable catalysts for preparing aldols/xcex1,xcex2-unsaturated nitriles/xcex1,xcex2-unsaturated esters/transesterified products/xcex2-nitroalkanols/Michael adducts and epoxides.
This invention particularly relates to an eco-friendly process employing recyclable LDH-diisopropylamide as an heterogeneous catalyst in place of soluble bases for preparing aldols/xcex1,xcex2-unsaturated nitriles/xcex1,xcex2-unsaturated esters/transesterified products/xcex2-nitroalkanols/Michael adducts and epoxides by reacting with corresponding aldehydes with acetone (Aldol condensation), aldehydes with activated nitriles or esters (Knoevenagel condensation), alcohols with xcex2-keto or simple esters (transesterification), aldehydes with nitro alkanes (Henry reaction), activated methylenes with xcex1,xcex2-unsaturated compounds (Michael addition), epoxidation of olefins. The obtained products are important intermediates for the preparations of drugs, pharmaceuticals, perfumes, cosmetics, oils, paint and fine chemicals. For example the products of benzylidene derivatives prepared by Knoevenagel condensation are used to inhibit tyrosine proteinase kinase, fine chemicals such as styrene oxide, 1-decene oxide, 1-octene oxide, 1-hexene oxide, cyclohexene oxide, cyclopentene oxide, epoxy chalcones by epoxidation of olefins, can be obtained by this method.
There are serious disadvantages in performing the reactions such as Aldol, Knoevenagel condensation, transesterification, Henry reaction, Michael addition and epoxidation of olefins with homogeneous system in the manufacture of aldols/xcex1,xcex2-unsaturated nitrites/xcex1,xcex2-unsaturated esters/transesterified products/xcex2-nitroalkanols/Michael adducts and epoxides due to presence of toxic wastes remnants of neutralization of soluble base with acid at the end of the reaction, lack of reusability and selectivity, tedious work-up procedure, higher temperatures and longer reaction times. By employing the heterogeneous catalytic system, the cost naturally comes down due to easy recovery and recyclability of the catalyst for number of recycles and very insignificant loss of active species, when compared with homogenous system. The products thus obtained using heterogeneous catalyst system are benign in the sense that the presence of minor impurities due to side reactions is also precluded.
Reference may be made to US patent U.S. Pat. No. 4,458,026 wherein aldol condensation of acetone is carried out by heat-treated synthetic anionic clay. The inherent disadvantages in this process are higher temperatures and longer reaction times with lower yields.
Reference may be made to Choudary et al., Chem. Commun., 1998, 1033 wherein aldol condensation of acetone is carried out by rehydrated hydrotalcite. The inherent disadvantages in this process are higher temperatures, longer reaction times and lack of selectivity.
Reference may be made to Choudary et al., Tetrahedron. Lett., 1998, 3555 wherein aldol condensation of acetone is carried out by Mgxe2x80x94Alxe2x80x94O-t-Bu hydrotalcite. The inherent disadvantage in this process is the catalyst is more sensitive to moisture and shelf life is short.
Reference may be made to J. Otera Chem. Rev., 1993, 93, 1449 wherein transesterification of alcohols are reviewed detailing many procedures under homogeneous and heterogeneous routes. The inherent disadvantages in these processes are higher temperatures, longer reaction times, and lack of selectivity and reusability.
Reference may be made to US patent U.S. Pat. No. 5,350,879 wherein transesterification of alcohols is carried by calcined hydrotalcites in heterogeneous way. The drawback of this process is the reaction is carried at higher temperature.
Reference may be made to Choudary et al., J. Mol. Catal., 2000, 159, 411 wherein transesterification is carried out by Mgxe2x80x94Alxe2x80x94O-t-Bu hydrotalcite. The inherent disadvantage in this process is the catalyst is more sensitive to moisture and shelf life is short.
Reference may be made to Choudary et al., Tetrahedron. 2000, 56, 9357 wherein Knoevenagel condensation and Michael addition is carried out by Mgxe2x80x94Alxe2x80x94O-t-Bu hydrotalcite. The inherent disadvantage in this process is the catalyst is more sensitive to moisture and shelf life is short.
Reference may be made to Choudary et al., Synlett., 1998, 1203 wherein epoxidation of olefins is carried out by Mgxe2x80x94Alxe2x80x94O-t-Bu hydrotalcite. The inherent disadvantage in this process is the catalyst is more sensitive to moisture and shelf life is short.
Reference may be made to Choudary et al., J. Mol. Catal., 1999, 146, 279 wherein Michael addition is carried out by Mgxe2x80x94Al rehydrated hydrotalcite. The inherent disadvantages in this process are low yields, longer reaction times and require activation for each catalytic cycle for reuse.
Reference may be made to Choudary et al., Green. Chem., 1999, 187 wherein Henry reaction is carried out by Mgxe2x80x94Al rehydrated hydrotalcite. The inherent disadvantages in this process are low yields, longer reaction times and require activation for each catalytic cycle to reuse.
The main object of the present invention is to prepare a heterogeneous recyclable LDH-diisopropylamide and use in catalytic amounts for preparing aldols/xcex1,xcex2-unsaturated nitrites/xcex1,xcex2-unsaturated esters/transesterified products/xcex2-nitroalkanols/Michael adducts and epoxides which obviates the drawbacks as detailed above.
Another object of the present invention is that LDH as synthesized having interstitial anions such as chloride, nitrate, carbonate, sulfate or calcination of LDH having the said interstitial anions at temperatures in the range of 350 to 550xc2x0 C. is used as precursors for the preparation of LDH-diisopropylamide.
Still another object of the present invention is to recover the heterogeneous LDH-diisopropylamide used in Cxe2x80x94C bond forming reactions comprising Aldol, Knoevenagel. Michael, etc, transesterification and epoxidation by simple filtration and reuse for number of cycles with consistent activity and selectivity.
Still another object of the present invention is the quantity of LDH-diisopropylamide used in the reaction contains 1 to 10 mol % of diisopropylamide with respect to the substrate.
The novelty of the present invention lies in the design and preparation of LDH-diisopropylamide through simple exchange process for the first time and its use in catalytic amounts for preparing aldols/xcex1,xcex2-unsaturated nitrites/xcex1,xcex2-unsaturated esters/transesterified products/xcex2-nitroalkanols/Michael adducts and epoxides. Higher yields were obtained when LDH-diisopropylamide catalysts are used in the Cxe2x80x94C bond forming epoxidation, and transesterification reactions in organic solvents. The products obtained by various methods are important intermediates for the preparation of drugs, pharmaceuticals, perfumes, cosmetics, oils, paints and fine chemicals. The consistent activity for several cycles in Cxe2x80x94C bond formation reactions makes the processes economical and possible for commercial realisation. Therefore, LDH-diisopropylamide is better option for the synthesis of aldols/xcex1,xcex2-unsaturated nitrites/xcex1,xcex2-unsaturated esters/transesterified products/xcex2-nitroalkanols/Michael adducts and epoxides. Thus this invention offers the best techno-economic route for the synthesis of intermediates in the preparation of drugs, pharmaceuticals and fine chemicals. The use of different metals and in varied compositions used in the preparation of LDH support has showed little impact on its final form of LDH-diisopropylamide with respect to activity.